The invention relates to a self-sealing spin pack for a spinner head of a spinning machine for spinning endless filaments from a viscous spinning liquid at high pressure. The invention includes a spinneret holder, in which a spinneret is inserted and is covered by a filter pack, a piston-like thrust piece, axially movable in the spinneret holder, having a central channel, the top of which borders the bottom of a distributor block which has at least one channel, a top seal between the thrust piece and the distributor block, a middle seal to seal the space above the filter pack against the spinneret holder and a bottom flat ring seal for sealing the spinneret holder at the bottom.
A self-sealing spin pack and its mode of action are disclosed by EP-A2-0 300 120 and EP-B1-0 163 248. This known spin pack can also further have a distributor plate (perforated plate) between the spinneret and the filter pack, which distributor plate has a potlike shape at the top to receive the filter pack (EP-B1-0 163 248; position 27).
This known spin pack is expensive and complicated in construction and has led in factory use to considerable problems and difficulties. As a result of the top seal, a gap is formed between the top of the thrust piece and the bottom of the distributor block. As a result of high melt pressure, high extrusion pressure and high melt temperatures, a gradual deformation and loss of the seal by flow of the sealing material into this gap occur. As a result of this, a dead space is formed, in which, because of the high residence time of the melt, polymer degradation occurs. Furthermore, leakages keep occurring at this position. The same problems, that is deformation and tearing of the seal, the formation of dead spaces (stagnant zones), polymer degradation and leakage, also occur in particular at the metal membrane seal (which is furthermore expensive to manufacture) and accordingly also at the bottom seal. This known spin pack thus has in total three seals, two of which are inadequate, of which one, the metal membrane seal, is relatively expensive. A further disadvantage arises in that as a result of the membrane seal, a relatively large free space is formed below the seal, which leads to an undesirable long residence time of the spinning liquid, in particular in the case of low filament deniers, which causes an undesired change in the same, polymer degradation and the like.